Dispensing containers come in many shapes and sizes. A particular problem associated with pressurized liquid dispensing containers, but not limited thereto, is the difficulty of determining the level of liquid present within the container. Such containers typically comprise a valve for dispensing liquid from the container and a vessel containing the liquid under pressure. The vessel is typically manufactured from impact extruded aluminium or rolled and welded sheet steel. Such materials are opaque making it impossible to see the quantity of liquid in the container. The quantity of liquid in the container also cannot easily be determined by handling, feel or sound of the container.
This problem is particularly evident in the medical field and particular in relation to inhalers used for respiratory conditions such as asthma. It is critical that a person suffering from a respiratory condition has access to inhalers to relieve symptoms such as being short of breath. Not being able to assess the volume of a medicinal product in an inhaler container is problematic as the user of an inhaler would not be able to identify when they need to order a new inhaler or assess whether the inhaler has dispensed the number of doses that it contains. Thus it is not uncommon for person's suffering from respiratory conditions to either run out of their inhaler before they order a new one or order a new one and dispose of the old inhaler before it is empty thus wasting the contents. A common inhaler used for relieving symptoms of asthma is labelled as containing 200 doses although such a container may contain enough medicine for approximately 240 doses. The inhaler is not provided with a dose counter hence an average user would be unaware when the inhaler is empty, or nearly so. Once around 200 doses have been metered, the inhaler will still dispense medicine but it will not dispense medicine at the recommended or specified dosage. Such a combination of medicine and propellant may not be sufficient to relieve symptoms of asthma leading to continuing, and potentially worsening, respiratory symptoms or may not be an effective treatment dose.
There are several methods of approximating the contents of inhalers which are not provided with dose counters. The most common are: shaking the can and listening to the contents moving, weighing the can by hand, observing the quality or strength of the spray and general observations on effectiveness. None of these methods can provide an accurate approximation of the contents of an inhaler.
WO2011/095761 provides solutions to the problem of not being able to determine the quantity of liquid in a pressurized liquid dispensing container.
The present invention seeks to provide a system for determining the quantity of liquid present in a dispensing container, particularly a dispensing container for dispensing medicine.